What Octane to use in my car?
Here is an email I recieved the other day from a cool car owner in Canada…
Hi, Kevin;
I came across your comments regarding octane while browsing the web for
fuel system info, and I disagree with you on this subject; your
contention that if the owners manual says ‘use 87′, then you suggest
that using premium fuel is ‘throwing money out the window’.
I used to feel that way, and could not find a definitive answer
anywhere (just opinions), so I set up a simple experiment back in 1987.
I bought a brand new car (Chevrolet Cavalier, Z24 model, with the 2.8L
V6 and a three-speed automatic transmission). This was a company car,
so my company paid for the fuel… and I ran it on nothing but Sunoco
94 Ultra, the highest octane fuel I could find in Canada; the manual
said to run it on regular, 87-grade unleaded gas.
Thousands and thousands of these cars were made and sold in north
america, so that was my base of comparison; when I finished the
experiment sixteen years, – and 330,000kms – later (when the car had
rusted away to the point of being unsafe), the following items were
still original, and unserviced..
The catalytic converter, the O2 sensor, the fuel pump, the fuel
injectors, the fuel rails, and the cylinder heads and valve-train.
Compression was still excellent on all cylinders. My dealer assured me
that at the ten-year mark (around 220,000kms) mine was the only ‘87
Cavalier that remained unserviced for fuel injector issues, and my car
was still flying through the bi-annual emissions test with great
numbers… right to its’ rusty end.
I put this down to several factors. One, Sunoco 94 can contain up to
10% ethanol (even back then!), and that I think aids in volatility and
with a fast ignition sequence. Second, Sunoco has a much more advanced
detergent-pac of additives in its’ premium fuel, and that eliminated
varnish from the injectors, pumps, and lines. Third, the greater heat
and faster flame-propagation of premium fuel eliminates (or greatly
reduces) carbon-build-up in the chamber and on the valves.
Was it a cost-effective experiment? I’d argue that it was, because the
cost of the catalytic converter alone exceeded the premium price I was
paying for gas (typically, 12¢ a litre more) annually. In fact, it
would have taken three to four years’ worth of my higher fuel costs to
equal the price of one converter… and the cost of having the
fuel-injectors serviced was about $800, and typically cars like mine
running on regular-grade needed this work every 100,000kms or so.
When I crunched all the numbers at the end of the experiment, it came
out as pretty much a wash (virtually even), but I completely escaped
the unpleasantness of unscheduled service visits due to vehicle failure
or poor emissions. That, and the fact that the car always ran great,
assured me that there was indeed a real value in burning nothing but
the best fuel available.
Now that I pay for my own fuel, I still use nothing but the very best,
highest octane… and that includes the diesel I put in my smart car,
too. And still, no run-ability issues with any of the family fleet.
So I think there actually is a difference, and a very real benefit…
but only after conducting that 16 year experiment!
Cheers, Malcolm (Canada)
And my response…
Malcolm,
I commend you on getting a cavalier to over 200,000 miles, it’s a testimate to your religious maintenance and care for the vehicle. I also thank you for taking the time to share your experiences with me. I have a few comments to add to the discussion…
1. I agree with your observations on better detergents in higher grades of fuel. I used to work at a Texaco station in High School and found better gas mileage using premium fuel over regular in my 1979 Ford Mustang. However since that time (late 80’s) the EPA has mandated higher detergent levels in all grades of gasoline. Texaco has since upped the detergent levels in their regular gasoline as have other brands. The major reason I got better mileage was probably because the engine had many miles on it and the carbon buildup in the combustion chamber mandated a higher octane rating.
2. A higher octane gasoline will actually burn slower ! This helps to prevent knock and also results in better combustion. It does not burn hotter, unless it’s in an engine with higher compression designed for a higher octane fuel.
3. For your experiment to really be valid, you would have had to have purchased an identical car and run regular fuel in it. I know this is being picky, but there could have been other factors effecting your outcome. The fact that you kept buying the same fuel is a big thing… by consistently buying fuel from a name-brand station, you assured a higher quality of fuel over the life of your vehicle. I always tell my visitors to be consistent in their purchase of fuel and even oil to keep their vehicles running their best.
4. My final comment to you and people reading my blog, would be to go with the lowest octane available that has a good level of detergents and meets the requirements set by your vehicles manufacturer. How can you tell which fuels have good detergent levels? Well the top tier gasoline program http://www.toptiergas.com/ is a good place to start. To be a top tier supplier, the gasoline companies must meet a stringent standard set my some of the top automobile manufacturers. This standard must be met by all grades of gasoline met, so it’s ok to run regular gasoline if your owners manual recommends it and you will still get the benefits of a higher detergent level.
One interesting note, if you look at http://www.toptiergas.com/ Sunoco Canada is on the list, but not the U.S. Company. This may be because of EPA regulations or tigher Canadian standards, which may or may not be part of the equation when looking at your experiment.
Take Care,
Kevin Schappell
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